Étude de la dissociation, par le désoxycholate de sodium, des polyparticules ribonucléoprotéiques nucléaires du cerveau de rat

The action of sodium deoxycholate (10g/l) on nuclear particles containing DNA‐like RNA from rat brain was studied. Under our experimental conditions, the size of the RNA remained unchanged when the particles were treated with deoxycholate. Therefore, modifications of the properties of the particles cannot be attributed to the release of latent RNAases by the detergent. The density, in CsCl, of the particles increased from 1.40 to 1.46–1.64 g/ml and their sedimentation coefficient decreased 30 to 50%, depending on the conditions of treatment with deoxycholate. It was calculated that an average 65% loss of proteins (as determined by density measurements) should cause a 32% reduction in the sedimentation coefficient of 150 S particles; the observed reduction was 39%. The agreement indicates that deoxycholate did not reveal hidden breaks in RNA, but only released proteins. Native particles were converted to 40‐S monoparticles upon mild ribonuclease hydrolysis, as is already known. Their density decreased slightly (from 1.41 to 1.39 g/ml) corresponding to a 10% loss of RNA. Complexes of a density between that of particles and released proteins were never observed. Such complexes would be expected if the RNA was progressively hydrolysed without modification of the protein moiety. In contrast, when the enzymatic action was allowed to proceed, particles disappeared progressively without further change in density. The behaviour of deoxycholate‐treated particles upon ribonuclease hydrolysis was different. The enzyme transformed the treated particles of high density (1.48 g/ml) into 5–20 S ribonucleoproteins of density 1.40 g/ml. Complexes of lower density were not detected. The appearance of fragments of density similar to that of native particles during RNAase action on treated particles, as well as the absence of complexes of density lower than 1.39 g/ml during RNAase action on native particles, are in favour of the type “folded ribonucleoprotein strand” structure for the monoparticle. The experimental results are in contradiction with the informofer structure proposed by Georgiev's group. The reasons for the discrepancy are not clear.